Servo operated actuating devices



Nov. 12, 1963 M. J. BROAD SERVO OPERTED ACTUATING DEVICES 3 Sheets-'Sheet l Filed March 27, 1961 Nov. 12, 1963 M. J. BROAD v 3,110,321

. SERVO OPERA-TED ACTUATING DEVICES Filed March 27, 1961 3 Sheets-Sheet 2 l To/eQuf Mom Nov. l2, 1963 M. J. BROAD 3,110,321

sERvo OPERATED ACTUATING DEVICES Filed March 27, 1961 3 Sheets-Sheet 5 Unted States Patent O 3,110,321 SERV@ UPERATED ACTUATING DEVCES Michael John Broad, Enlield, England, assigner to The Plessey Company Limited, London, England, a British company Filed Mar. 27, 1961, Ser. No. 98,707 8 Claims. (Cl. 137-59615) rIlhis invention relates to fluid-pressure servo actuating devices and has for an object to provide an improved actuating device in which movement of a control or primary element requiring little actuating force produces, by servo action, movement of a fluid-pressure motor in a direction and by an amount determined by the movement of the primary element.

According to the invention the huid-pressure motor comprises two piston elements acting against each other, fluid being admitted to both piston elements in parallel from a common source of fluid under pressure, and fixed meterin gapertures being provided in fthe respective admission lines to `each piston element, while fluid is allowed to spill from each of these admission lines through two variable ports of which one is controlled by the control element and the other by a feed-back element operated in such direction by the movement of the piston elements that the movement of the piston elements as a result of a displacement of the control element will alter the sizes of the apertures controlled by the feed-back element in the opposite sense to that in which the sizes of the other apertures have been altered by the movement of the control element. The two apertures cooperating with the control element may be arranged on a ilat surface at one side and the two apertures co-operating with the feed-back element on a second iat surface at the opposite side, of a valve seat member, the control element and the feed-back element being formed as rotatable, approximately D- shaped plates respectively co-operating with the two said surfaces of the valve-seat member, or alternatively said apertures may be provided in an internal or external surface of revolution, for example in a cylindrical surface or in co-afial cylindrical surfaces, the oriices controlled by the feed-back element being axially displaced in the direction of the cylinder axis from the oriiices controlled by the control element, while the control element and feed-back element are constituted by rotary slide elements of complementary shapes cooperating with the said surface or surfaces. IIn each case the movement of the control element in one direction will cause the pressure acting on one of the piston elements to rise and the pressure acting on the other to fall, thus producing forward movement of one and reverse movement of the other piston element until the resultant displacement of the feedback element has produced equal and opposite variation of the apertures controlled by the latter, thus again equalising the pressure acting on the two piston elements. Since the movements of the control and feed-back elements are rotary, it is possible, by simply placing the apertures respectively controlled by the control element and the feed-back element at different distances from the axis of rotation while making them of equal size, to arrange for the angular movements of the feed-back element to be a multiple or a fraction or" the movements of the control element.

The piston arrangement may be utilised as a ow-control device governing the flow .from a source of pressure to, and the release of pressure fluid from a load, or the simultaneous admission of fluid under pressure to one, and its return from another load or vice versa. The Volumes of flow controlled in this manner may be many times greater than those which can be controlled directly by the control element. The two loads may be respectively con- "ice stituted by the two sides of a hydraulic motor which operates in one direction or the other according as hydraulic fluid is admitted to one and allowed to escape from the other side or vice versa.

In the drawing accompanying the specication,

FIGURE 1 is a somewhat diagrammatic sectional elevation, in section on line 1--1 of FIGURE 2, of one embodiment of the invention in which the two piston members serve as secondary flow-control elements, operate in parallel bores, and act upon, and are coupled together by, a rocker member constituting the feed-back element,

FIGURE 2 is a section on line 2 2 of FIGURE l,

FIGURES 3 and 4 are respectively an elevation, in section on `line @-13 of FIGURE 4, and a section on line 4 4 of FIGURE 3, of a modified embodiment,

FIGURE 5 is an enlarged cross-section of the control device Iof the said modified embodiment, and

FIGURE, 6 is an enlarged somewhat diagrammatic perspective view thereof,

FIGURE 7 is a diagrammatic elevation of a modification of the embodiment illustrated in FIGURE `1 in section along the axes of the piston elements, and

FIGURE 8 is a perspective view, partly broken away, of a modied control device, which may be substituted for that of the embodiment illustrated in FIGURES 3 to 6.

Referring now rst to FIGURES 1 and 2, the device according to the invention comprises a housing 1 having two parallel cylinder bores 2 and 3 of equal diameter accommodating piston members 4 and 5 respectively acting on a rocking platform 6 at opposite sides of the axis of the latter. The housing is provided with an inlet 7 for the hydraulic liquid, from which two passages -8 and 9 branch off which respectively, through iixed metering oriices 10 and 1d, lead to the cylinder bores 2 and 3. Branch lines i12 and 13 respectively lead from each passage `8 and 9 to two equal-sized ports 14 and 1S or 16 and 17 on opposite flat valve seat surfaces 18 and 1'9 of a valve seat member 20. An approximately D- shaped plate 2-1, hereinafter called D-plate, and acting as the valve element slides sealingly on the seat surface 18. It constitutes the control member and is coupled by a shaft 22 to a diagrammatically indicated electric torque motor 23 by which i-t is turned in one direction or the other by a variable ang-le according to the intensity and direction of the torque produced by the motor. A similar and oppositely facing valve plate 24, attached to the rocking member 6, slides :sealingly on the opposite valve face 19 of the Valve-seat member 20 and constitutes the feedback member. In the drawing a small gap is left between surfaces `1S and `19 and the surfaces sliding thereon, to show the individual elements more clearly. The ports 14, 16 which cio-operate with the control valve member 21 are spaced further from the common axis of the shaft 2v2 and the rocker 6 than the ports 15 and 17 which cooperate with the feed-back member 24, land the hou-sing 1 is further provided with a drain aperture Z5 for the withdrawal of liquid lthat has spilled through the apertures 1:4, 1S, 16 and A17. Furthermore, each ofthe piston members 4 and 5 is provided with a land 26 and 27 respectively which not only guides the stem off the piston in its bore but also co-operates with a load outlet 28 or 29 to con nect the latter either with a chamber enclosed between the piston proper 4 or 5 and its control land 26 or 27, or with a cavity 3i? in the lower part of the housing 1, which communicates with the drain aperture 25. The chamber formed between each piston and its control land communicates through a cross bore 31 with the inlet 7 for the hydraulic pressure liquid.

Assuming now that, due to operation of the electric torque motor 23, the D-plate 21 (ie. the control element) has been turned by a small angle in an anti-clockwise direfction as seen in FIGURE l.y This will cause lhe eX- p'osed part of the opening of port 14 to be increased and that of port 16 to be correspondingly decreased, thus, increasing the ilow through and the pressure drop in the metering olriice and hence reducing the pressure in Vbore v12 which acts 'on piston element 4 and at the same time decreasing the flow through and the pressure drop in the orifice 1.1 and hence increasing the pressure in bore 13 which acts on piston element 5. Piston element 5 will move downwardly and turn the rocker 6 in a clockwise direction as .seen in FIGURE 1, moving the piston 4 npwardly against the reduced pressure acting thereon. The resulting movement of the rocker 6 will turn the D-plate 24, i.e. the feed-back element, which is connected therewith, and will continue until, due to this movement of the D-plate 24, the part of port 15 not covered by the latter is decreased by the same amount by which the noncovered part of port 14- has been increased, and similarly the opening of port 17 has been increased by the same amount by which that of the por-t -16 was increased by the movement of the control plate 21. When this position is reached, the total outlet areas available at the outlet end of each of the bores 12 and 13 will again be equal, and the pressures in these bores and tho-se acting on the piston elements 4 and S will therefore likewise be equal to each other thus terminating the movement of the piston elements. Such termination of the movement of the piston elements after a predetermined length of stroke is independent of the provision of any springs counteracting such movement, whereby the invention avoids the necessity of providing a pair of matched springs. Moreover, vsince only the difference between the pressure drops in orices 10 and 11 is utilised, the operation of the device remains substantially unaffected if there is slight leakage between surfaces .18 and 19 and the surfaces sliding thereon. It is therefore possible to make the frictional resistance to movement of plate 2.1 very small, so that an appreciable output torque can beV achieved with very little resistance to the movement of the torque motor 23. Furthermore it will be :seen `that the resulting movement .of the rocker 6 at which the D-plate 24 (i.e. the feedback element) restores pressure balance and thus terminates further movement, is proportional to the original movement of the control element 21 but is proportionally greater in View off the fact that the radial distance of the ports 15 and 17 which are controlled by the feed-back D-plate 24, is smaller than that of the ports 14 and 16 controlled by the control element 21 so that since the diameters of the ports 14, 15, 16 and 17 are equal, a proportionally greater movement of therfeed-back element 24 is necessary Vto produce the same variations in the non-covered cross-sections of ports 15 and v17 as have been produced in ports 14 and 16 by the original movement of the control element 21.

The displacement of the piston elements 4 and 5 just described also moves the lands .26 and 27. Land 27 moves downwardly so as to partly open load port 29 to the pressure chamber formed in cylinder bore 3 between the piston 5 proper and land 217, and thus to liquid admitted through inlet 7, while the movement of land 26 is upward and similarly permits a restricted ow from load connection 2S to drain chamber 3.0. Thus, if load lines 28 and 29 are connected to the two sides of a hydraulic motor, the operation just `described will cause the hydraulic motor to rotate in a direction corresponding to a dow from 29 to 28 and at a speed dependent upon the amount of displacement of the control lands 27 and 26, while the displacement of pistons 4 and 5 in response to an oppositely directed angular displacement of control element 21 will'cause the hydraulic motor to rotate in the opposite direction.

In each case when the control shaft is returned to its normal central position, pressure balance is again disturbed in the opposite direction and will eventually be restored when the rocker member 6 has likewise assumed its normal symmetrical position.

When it is preferred to use cylinder surfaces instead of flat surfaces for the control of pressures in branches 12 and 13, the two-face slide-valve assembly 2t), 21, 24 may be replaced by a cylindrical valve assembly as is illustrated in FIGURES 3 to 6, in which corresponding elements bear ythe same reference numerals as in FIGURE 1, increased by 1211. In this embodiment the two-sided flat body 2i? of FIGURES 1 and 2 has been replaced by a stepped cylindrical body 149 the interior of which constitutes the drain housing 159, while the surfaces 133 and 13g of the stepped bore of this'body replace the at surfaces of the body 2? by cri-operating respectively with rotary half-sleeves 141 and 144, of which the former is operated via shaft 142 by the torque motor 143, While the latter is operated by the pistons 124 and 125 via the rocking beam 125.

Assuming that the torque motor 143 has turned'th'e half-sleeve 41 which constitutes the rotary control valve, by a small angle from its neutral position in a clockwise direction as seen in FIGURES 3 and 6, the leading edge (counting in the direction of displacement from the neutral position) of the half-sleeve 41 will cover a greater part of port 136 while its trailing edge will cover a smaller part of port 134 compared with the neutral position, with the result that the flow in line 133 is decreased and that in line 132 is increased. Since the former iiow passes through restriction 131V on its way to port 135 and the latter passes through restriction 139 on its way to port 134, the consequence is a reduced pressure drop in the first-mentioned restriction and an increased pressure drop in the last-mentioned restriction. The pressure acting on piston will therefore rise and that acting on piston 124 will decrease compared with the neutral position of the valve 141, thus causing the pistons to turn the beam 126 about its pivot axis in a clockwise direction. This rotary displacement of the beam 126 causes the leading edge of rotary valve 144 to cover a greater portion of port and its trailing edge to clear a greater portion of port 137. The movement of the pistons and beam Will continue until the increase in the available area of port 137 balances the reduction in the available area of port 135 and at the same time the decrease in the available area of port 135 will balance the increase in the available area of port 134, thus restoring the original flow conditions through restrictions 131 and 134) andV thus the balance of the pressures acting respectively on pistons 125 and 124;. The movement of the pistons is utilised, in exactly the manner described with reference to FIGURES 1 and 2, for the control of 110W in the service lines 148 and 149 as will now be understood without further detailed description.

While two embodiments of the invention have hereinabove been described in some detail, various features of these embodiments may be modified within the scope of the present invention. Two particular modifications shall now be described with respective reference to FIGURES 7 and 8 of the accompanying drawing.

While in the embodiment illustrated in FIGURES 1 and 2 the two oppositely acting piston eiements are arranged side by side and coupled by the rocker lever 6, FIGURE 7 illustrates an arrangement which in most other respects is similar to that illustrated in FIGURES l and 2, but in which the two fuel-control pistons are arranged in mutual axial alignment. Corresponding parts have been indicated by reference numerals which are distinguished from those used in FIGURES l and 2 by the addition of the letter a; the two ends of the duct 31 through which fluid pressure is admitted between the lands of each of the spool-type slide valves have been respectively marked 31a and 31h. It will be appreciated that elements not shown in FIGURE 4 are supposed to be constructed as shown in FIGURE 1, more particularly the connection of ducts 8a and 9a to the iluid pressure inlet 7 through restrctors such as shown at 119 and 11 in FIGURE 1 and the provision of ducts, such as ducts 12 and i3 of FIGURE 1, which lead from passages 3a and 9a to the ports controlled by members 2in and 24a.

FIGURE 8 illustrates a modified control device which may be substituted for that of the embodiment of the invention illustrated in FGURES 3 to 6, and which avoids the need of providing a stepped bore. The stationary stepped sleeve 148 of FlGURES 3 to 6 is replaced by a cylindrical sleeve 46a which has a pair of control ports 34a, 36a spaced along one generatrix and a pair of feed-back ports 35a and 37a respectively in diametric opposition to the control ports. Two rotary valve elements 51 and 54 are arranged for rotation about a common axis, the one valve element El being lixed on the shaft 42a of the torque motor 23, and constituting the control valve element, while the feed-back valve element S4 is rigidly connected with a lever arm 6c the function of which corresponds to that of beam 126 in that it co-operates with a pair of pistons 64 and S acting upon it in opposition to each other. he ports 34a and 35a are connected with passage 132 and the ports 35a and 37a are connected with passage 133, while the connections between these passages and the pistons 6a and 65 and the co-operation of the pistons with the liquid supply and the service ports is identical to that described with reference to FIGURES 3 to 6 and need therefore not be described ln operation, assuming that the control valve element 51 has been turned by a small amount in a clockwise direction as seen in FlGURE 8, this will reduce the exposed area of port 37a and increase that of port 35a, thereby reducing the flow in passage 133 and the pressure drop in restriction 131 and increasing the ilow in passage 132 and the pressure drop in restriction 139, so that piston 65 will advance and piston 64 will recede with the result that feed-back valve element 54 will also be moved in a clockwise direction so as to decrease the available cross-section of port 34:1 and increase that of port Since port 34a is connected in parallel with port 35a and port 35a in parallel with port 37a, equal pressure action upon the two pistons 64 and 65 will be restored when the exposed area of port 36a has been increased by the same amount by which that of port 37a was decreased and conversely the area of port has een decreased by the same amount by which that of port 35a had previously been increased.

What I claim is:

1. A fluid pressure-servoactuating device, comprising a fluid pressure motor having two piston elements acting in opposition to each other, huid-pressure admission means leading to both piston elements in parallel, two xed metering apertures, one in the respective admission line to each piston element, two spill passages each communicating with one of these admission lines at a point between the respective metering aperture and piston element and each including two parallel slide valve ports, a rotary control valve element which co-operates with one port', and a feed-back rotary valve element which co-opcrates with the other port of each spill passage, said control element and said yfeed-back element being each slidably movable across said ports, and each having two edges respectively co-operating with the ports of the two spill passages and facing respectively forwardly and backwardly in relation to the direction of movement of such element so that any movement of either element will increase the spill from one and reduce the spill from the other admission line, the feed-back element being so `coupled with the fluid pressure motor that the pressure variation produced bya movement of the motor and feed-back element will oppose such movement of the motor.

2. An actuating device as claimed in claim 1, wherein the two ports co-operating with the control element are arranged on a hat surface at one side and the two apertures -co-operating with the feed-back element on a second llat surface at the opposite side, of a valve seat member, the control element and the feed-back element being formed as approximately D-shaped plates respectively co-operating with the two said surfaces of the valveseat member.

3. An actuating device as claimed in claim 1, wherein the two ports co-operating with the control element are provided in a surface of revolution, the orifices `co-operating with the feed-back element being axially displaced in the direction of the axis of said surface from the oriices controlled by the control element, the control element and feed-back element being constituted by rotary slide elements of complementary shapes co-operating with the said surface.

4. An actuating device as claimed in claim 1, wherein the two ports co-operating with the control element are provided in a cylindrical sleeve, the onices co-operating with the feed-back element being axially displaced in the direction of the cylinder `axis from the oris controlled by the control element, the 'control element and feedback element being constituted by rotary slide elements of complementary shapes co-operating with the said surface.

5. A11 actuator device as claimed in claim 1, wherein the two ports Ico-operating with the control element are provided in a cylinder sleeve, the orices cooperating with the feed-back element and the orifices controlled by the control element being respectively axially displaced from each other in the direction of the cylinder axis, and the orifices :co-operating with the feed-back element being arranged in substantially diametric opposition to the orices controlled by the control element, the control element and feed-back element being constituted by rotary slide elements of complementary shapes co-operating with the bore of said sleeve, each slide element having two axially adjacent portions respectively having control edges facing in opposite directions for respective cooperation with the two bores associated with the slide element.

6. Actuating device as claimed in claim l, wherein the ports respectively controlled by the control element and the feed-back element are arranged at different distances from a common axis of rotation while making them of equal size, to arrange for the angular movements o the feed-back element to be a multiple or a fraction of the movements of the rcontrol element.

7. Actuating device as claimed in claim l, wherein the fluid-pressure motor is constructed as a flow-control device governing the flow from a source of pressure to, and the release of pressure lluid from a load.

8. Actuating device as claimed in claim l, wherein the iiuid-rressure motor -is constructed as a llow-control device governing the simultaneous admission of fluid under pressure to one, and its return from another load and vice versa.

References Cited in the le of this patent UNITED STATES PATENTS 2,709,421 Avery May 31, 1955 2,835,265 Brandstadter May 20, 1958 2,926,696 Kolm Mar. l, 1960 2,998,804 Clement Sept. 5, 1961 FGRElGN PATENTS 581,925 Great Britain Oct. 30, 1946 

1. A FLUID PRESSURE-SERVO-ACTUATING DEVICE, COMPRISING A FLUID PRESSURE MOTOR HAVING TWO PISTON ELEMENTS ACTING IN OPPOSITION TO EACH OTHER, FLUID-PRESSURE ADMISSION MEANS LEADING TO BOTH PISTON ELEMENTS IN PARALLEL, TWO FIXED METERING APERTURES, ONE IN THE RESPECTIVE ADMISSION LINE TO EACH PISTON ELEMENT, TWO SPILL PASSAGES EACH COMMUNICATING WITH ONE OF THESE ADMISSION LINES AT A POINT BETWEEN THE RESPECTIVE METERING APERTURE AND PISTON ELEMENT AND EACH INCLUDING TWO PARALLEL SLIDE VALVE PORTS, A ROTARY CONTROL VALVE ELEMENT WHICH CO-OPERATES WITH ONE PORT, AND A FEED-BACK ROTARY VALVE ELEMENT WHICH CO-OPERATES WITH THE OTHER PORT OF EACH SPILL PASSAGE, SAID CONTROL ELEMENT AND SAID FEED-BACK ELEMENT BEING EACH SLIDABLY MOVABLE ACROSS SAID PORTS, AND EACH HAVING TWO EDGES RESPECTIVELY CO-OPERATING WITH THE PORTS OF THE TWO SPILL PASSAGES AND FACING RESPECTIVELY FORWARDLY AND BACKWARDLY IN RELATION TO THE DIRECTION OF MOVEMENT OF SUCH ELEMENT SO THAT ANY MOVEMENT OF EITHER ELEMENT WILL INCREASE THE SPILL FROM ONE AND REDUCE THE SPILL FROM THE OTHER ADMISSION LINE, THE FEED-BACK ELEMENT BEING SO COUPLED WITH THE FLUID PRESSURE MOTOR THAT THE PRESSURE VARIATION PRODUCED BYA MOVEMENT OF THE MOTOR AND FEED-BACK ELEMENT WILL OPPOSE SUCH MOVEMENT OF THE MOTOR.
 7. ACTUATING DEVICE AS CLAIMED IN CLAIM 1, WHEREIN THE FLUID-PRESSURE MOTOR IS CONSTRUCTED AS A FLOW-CONTROL DEVICE GOVERNING THE FLOW FROM A SOURCE OF PRESSURE TO, AND THE RELEASE OF PRESSURE FLUID FROM A LOAD. 